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All you need to know about the past, present and future of stereolithography

Today we refer to it as vat photopolymerization or VPP: the first ever 3D printing technology has ramified into many different evolutions

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Vat photopolymerization, specifically laser stereolithography or SL/SLA, was the first 3D printing technology on the market. Chuck Hull invented it in 1984, patented it in 1986, and founded 3D Systems. The process uses a laser beam to polymerize a photoactive monomer material in a vat. The photopolymerized (cured) layers adhere to a build plate that moves up or down depending on the hardware, allowing successive layers to form. SLA systems can also produce very small and precise parts using a small laser beam diameter, in a process known as micro SLA or µSLA. They can also produce very large parts using a larger beam diameter and longer production times, within build volumes measuring over two cubic meters.

The SLA-1 Stereolithography (SLA) printer, the first commercial 3D printer, was introduced by 3D Systems in 1987.

There are several variations of vat photopolymerization technology available today. The first to emerge after SLA was DLP (Digital Light Processing), developed by Texas Instruments and brought to market in 1987. Instead of using a laser beam for photopolymerization, DLP technology uses a digital light projector (similar to a standard TV projector). This makes it faster than SLA, as it can photopolymerize a whole layer of the object at once (referred to as a “planar” process). However, the quality of the parts depends on the projector’s resolution and degrades as the size increases.

Like material extrusion, stereolithography became more accessible with the availability of low-cost systems. The first low-cost systems were based on the original SLA and DLP processes. However, in recent years, a new generation of ultra-low-cost, compact systems based on LED/LCD light sources has emerged. The next evolution of vat photopolymerization is known as “continuous” or “layerless” photopolymerization, which is typically based on a DLP architecture. These processes utilize a membrane, typically oxygen, to enable faster and continuous production rates. The patent for this type of stereolithography was first registered in 2006 by EnvisionTEC, a DLP company that has since been rebranded as ETEC, following its acquisition by Desktop Metal. However, Carbon, a Silicon Valley-based company, was the first to market this technology in 2016 and has since established itself as a leader in the market. Carbon’s technology, known as DLS (Digital Light Synthesis), offers significantly higher productivity rates and the ability to produce parts with durable hybrid materials, combining thermosets and photopolymers. Other companies, such as 3D Systems (Figure 4), Origin (now part of Stratasys), LuxCreo, Carima, and others, have also introduced similar technologies to the market.

The original stereolithography patent.

Another technique belonging to the vat photopolymerization family is two-photon photopolymerization or 2PP. This method is used to create small features in a photosensitive material without the need for complex optical systems or photomasks. It relies on a multi-photon absorption process in a material transparent to the laser wavelength used to create the pattern. By scanning and modulating the laser correctly, a chemical change, usually polymerization, occurs at the focal spot of the laser, allowing for the creation of three-dimensional patterns. This method is marketed for the additive production of nanoscopic and microscopic objects.

VPP-specific key evolutionary trends

  • Development of larger SLA systems mainly by Chinese companies
  • Continuing growth in the adoption of high-speed DLP with higher content of durable (thermoset) materials
  • Batch production capabilities of up to several hundred thousand parts
  • Implementation of multiple systems in Chinese factories and by companies using Carbon DLS technology
  • Rapid commercial adoption of systems for micro parts, such as BMF and Fabrica Group (Nano Dimension)
  • Significant ongoing sales of mid-cost systems offered by Formlabs
  • Low-cost systems utilizing LCD technology sold in large unit numbers

3D Systems and several Chinese companies, including UnionTech and Kings3D, now offer commercial SLA systems with build volumes exceeding one cubic meter, and in some cases, up to two cubic meters.

Map of the leading vat photopolymerization thardware technologies and companies. Click on the map to view the interactive version.

Laser stereolithography (SLA)

Laser stereolithography is a process that utilizes a low-power laser beam as an energy source to trigger a photopolymerization reaction. This technology has both advantages and disadvantages. One notable disadvantage is the relatively high cost of the laser source and the complex mirror mechanism used to control it. Additionally, compatible materials tend to degrade over time when exposed to visible light, limiting the range of applications to prototypes and tools. However, using a laser also offers advantages, such as the ability to produce larger parts without compromising resolution and quality, as well as the capacity to expedite the build process by widening the diameter of the laser beam. Currently, laser stereolithography is employed in large industrial systems capable of printing parts larger than 1 cubic meter, which can cost over $1 million. It is also used in affordable prosumer systems that can be purchased for below $3,000.

Laser stereolithography or laser vat photopolymerization (SLA)

In laser stereolithography, thermoset resins are selectively cured layer by layer using an energy source, similar to other vat photopolymerization methods. In the SLA process, a low-power laser beam is used to initiate the photopolymerization reaction. In the “top-down” form of the SLA process, a liquid resin photopolymer is applied to the resin tank. A laser beam from above the tank is directed onto a series of mirrors or galvanometers. These mirrors control the beam’s direction as it interacts with the resin. By following computer instructions, the galvanometers accurately trace a 2D shape in the liquid resin. When the laser beam interacts with the photosensitive resin, the liquid solidifies, resulting in the creation of a solid shape. After completing a layer, the build platform moves downward, and a blade reapplies the tank with liquid resin. The laser then traces the next layer of the printed part, and this process repeats until the part is fully formed. Additionally, the resin’s polymerizable groups create cross-layer bonds, ensuring strength in all directions of the part.

While SLA systems, particularly desktop machines, may use a “bottom-up” configuration instead of a “top-down” one, the fundamentals remain similar. In bottom-up systems, the laser is located beneath the resin tank, which possesses a transparent bottom. Rather than moving downward, the build platform moves incrementally upward and out of the shallow pool of liquid resin. This arrangement allows the production of parts that surpass the size of the resin tank itself.

SLA parts typically require extensive support structures, which can be generated during part design. These support structures not only prevent deflection like in extrusion processes but also maintain the integrity of the SLA part while it is subjected to motion from the re-coater blade. Additionally, in bottom-up printing, the support structures help the part withstand the rocking motion of the vat that peels each layer from the build platform. After printing, the parts are rinsed and may undergo post-curing to form additional chemical bonds and improve mechanical properties. It is necessary to manually remove the support structures.

Key players and systems

Formlabs’ Form 1 SLA 3D printer launched in 2012.

Since the first SL-1 system was sold in 1988, 3D Systems has been the technological and market leader of the SLA segment, as well as one of the overall leaders in the global AM industry. Currently, the focus of the company’s SLA activities is on large-format machines primarily used for industrial parts, tooling, investment casting, and dental applications. Although 3D Systems remains the global market leader (due to its expansion into other technological segments, such as material jetting and powder bed fusion of polymers and metals), it has faced increasingly tough competition.

The first major challenge came from Formlabs, a Boston-based startup founded by MIT graduates. Formlabs was the first to introduce a sufficiently reliable low-cost prosumer SLA system to the market. Priced below $5,000, Formlabs’ Form 1, Form 2, and Form 3 3D printers have provided a viable low-cost solution in many industrial segments that were previously dominated by 3D Systems. These segments include the dental and jewelry industries, as well as tooling and prototyping across various sectors. While Formlabs has to pay 3D Systems an 8% royalty on everything it sells, following a 2014 settlement for a breach of eight SLA-related patents, the company has sold more units than any other SLA 3D printer manufacturer. Overall, 3D Systems and Formlabs remain market leaders for the industrial and prosumer segments, respectively.

DWS’s XFAB could have been the most credible competitor to the Form 1

Up until the mid-2010s, one of the most credible competitors to both 3D Systems and Formlabs, in terms of technology, was DWS, an Italy-based company. DWS initially provided systems to jewelry makers in the city of Vicenza, a major hub for jewelry manufacturing. Later on, they expanded into the dental and industrial parts segments and have established themselves in these areas of manufacturing.

Stratasys also entered the SLA segment in 2021 by acquiring the UK company RPS and now offers the Neo range of industrial SLA machines. Over the past five years, several Chinese companies have emerged as strong players in the global SLA market. Notable companies such as UnionTech, with over 5,500 system sales to date, and Kings 3D, now one of the largest 3D printer manufacturers and service providers in Asia, have made significant contributions. These companies now offer a wide range of large-format industrial machines at competitive prices. China has also seen the rise of multiple AM service providers, with factories housing hundreds of industrial SLA systems.

One of the most recent innovations in the market comes from Axtra 3D, a startup led by Founder and CEO Gianni Zitelli. They have developed the HPS (Hybrid Photo Synthesis) Light Engine, which addresses the limitations of SLA, DLP, and LCD technologies. By combining laser stereolithography with LCD or DLP processes, the HPS Light Engine enables high-speed production of high-resolution parts with smooth surfaces. Axtra 3D’s flagship product, the LUMIA 3D printer, incorporates this light engine technology. However, the HPS Light Engine can also be integrated into other DLP, SLA, or LCD 3D printers, including high-speed photopolymerization systems.

Table of key players and systems in SLA Stereolithography
CompanyLocationPolymer AM Hardware ProductsType of products
3D SystemsUSASLA750, ProX 950, ProJet 7000 HD, ProJet 6000 HDIndustrial (dental, jewelry)
StratasysUSA/IsraelNeo 800, Neo450s, Neo450eIndustrial
FormlabsUSAForm 3+ Form 3L, Form 3B+, Form 3 BLProsumer
UnionTechChinaRSPro line, Lite line, Pilot lineIndustrial
Kings 3DChinaKings 600, Kings 800, Kings 1700Industrial
DWSItalyXFAB line, 0XX line, XPRO lineIndustrial and prosumer
Axtra3DUSA/ItalyLumia X1, Revox X1Industrial

Digital light processing stereolithography (DLP)

DLP (Digital Light Processing) is a vat photopolymerization 3D printing technology that uses digital light projection instead of a laser beam to trigger the photopolymerization reaction. It was invented by Larry Hornbeck of Texas Instruments in 1987. DLP utilizes projectors commonly used for TV and movie projections, which brings both benefits and limitations.

One significant advantage of DLP is that it is a “planar” technology, enabling the creation of the entire layer at once. In contrast, other AM technologies like extrusion and laser-based methods construct point by point, making DLP theoretically much faster than SLA. However, this higher speed potential was not fully realized until the continuous DLP processes emerged (see next section).

DLP technology also has limitations. The resolution of DLP is directly tied to the resolution of the digital light projector used. This means that smaller DLP 3D printers can be quite affordable and they initially created the entry-level segment for photopolymerization. On the other hand, larger DLP 3D printers can be extremely expensive.

The DLP (Digital Light Processing) process is similar to SLA (Stereolithography). It uses an energy source and a system of mirrors to selectively cure a photopolymer resin and create a 3D object. Instead of using a laser beam, DLP uses a digital light projector. The light from the projector passes through a dynamic mask of tiny mirrors that can be moved to change the direction of the light towards the resin, ultimately curing it.

Stereolithography, aka vat photopolymerization or VPP, the first ever 3D printing technology, has ramified into many different evolutions.
Texas Instruments’ DLP process. Soruce: Texas Instruments

The process begins by adding a photopolymer thermoset resin to the tank and lowering the build platform just above the base of the tank. This small gap represents the effective layer height of the build. During DLP 3D printing, the projector doesn’t trace a 2D shape into the resin using a laser; instead, it projects the entire 2D layer into the vat at once, curing the entire layer. This makes the process faster than SLA. The projector flashes a series of these 2D images, each consisting of thousands of square pixels, onto the resin while moving the build platform in small increments between each projection. The resolution of the projector limits the quality of DLP-printed parts.

Most DLP systems have a bottom-up configuration, unlike SLA systems which can be either top-down or bottom-up. In a DLP system, the projector is situated underneath the transparent-bottomed resin tank, and the 2D images are projected upwards through the base of the tank onto the resin. The build platform moves upward with each successive layer, instead of downward. Like other vat photopolymerization technologies, DLP requires the use of extensive support structures, which can be generated during part design. After printing, parts are rinsed and may undergo post-curing to form additional chemical bonds and enhance mechanical properties. Support structures must be manually removed.

Key players and systems

The original market leader in traditional DLP technology is EnvisionTEC, which was acquired by Desktop Metal for $300 million in 2021 and rebranded as ETEC. EnvisionTEC was founded in 2002 by engineer entrepreneur Al Siblani, with his first patent submission for the technology filed in 1999. Sasha Shkolnik, who had previously worked with Siblani at Helisys, assisted in the development of the technology. EnvisionTEC’s initial 3D printer gained popularity in the jewelry market because of its precision and high-quality surface finish. From there, the technology expanded into other industries, including hearing aids, dental prosthetics, and other small and smooth parts.

ETEC’s Xtreme 8K DLP 3D printer.

ETEC remains a leader in its reference markets (prototyping, jewelry, dentistry) with its established Xtreme 8K, Pro XL, and D4K brands. The Xtreme 8K DL is now considered the largest production-grade DLP 3D printer in the world. It utilizes dual 4K projectors, allowing it to produce multiple nested builds per day with a 71-liter build envelope. It also supports a lineup of materials that includes polypropylene-based polymers and several elastomers.

DLP technology has experienced several developments, including the emergence of more affordable yet reliable systems. B9 Creations introduced one of the first such systems after a successful crowdfunding campaign, which lowered the cost of machines to around $15,000. Since then, numerous new machines have entered the market. One challenge for DLP technology has been its high cost, which has limited high-quality 3D printers to large-scale manufacturing settings. However, thanks to new technology introduced by Texas Instruments in 2021, a new level of affordable DLP technology is on the horizon. The new TI DLP Pico chipsets, developed to fit into smaller applications, allow engineers to create high-quality 3D printers that are more accessible and affordable.

These smaller TI DLP Pico chipsets are anticipated to make high-quality 3D printers small enough to be placed on desks at home or work. Consequently, they can be available for less than $500, which is less than half the price of previous DLP 3D printers. Anycubic in Shenzhen, China, was one of the first companies to take advantage of this technology and develop affordable 3D printers, such as their new Photon Ultra machine.

Another area of development is in the dental segment. While all DLP 3D printers are primarily used for jewelry and dental applications, some manufacturers have specifically developed systems for dental applications, such as Bego and SprintRay. Other manufacturers, like Ackuretta and Rapishape, target multiple segments but also have a particular focus on dental industry adoption.

An interesting development in DLP technology is the application of multiple projections on a single layer to achieve higher resolution, demonstrated in ETEC’s latest Xtreme 8K system.

Table of key players and systems in DLP stereolithography
CompanyLocationPolymer AM Hardware ProductsType of products
ETEC (Desktop Metal)USAXtreme 8K, D4K, Pro XLIndustrial and professional
ProdwaysFranceLD seriesDental 3D
B9 CreationsUSAB9 Core SeriesProfessional
RapidshapeGermanyI series, D series, S series and HA seriesIndustrial and professional
AckurettaTaiwanAckuray, DIPLOProfessional
SprintRayUSAPro DentalDental
BegoGermanyVarseo (XS, S, L)Dental
AnycubicChinaPhoton UltraConsumer

LED/LCD stereolithography

A major development in vat photopolymerization in recent years is represented the introduction of more affordable and/or faster LCD/LED-based digital light processing technology. LCD 3D printers use an LCD display module to project a light pattern that cures resin in the vat. LED light from a lamp is used as the light source while the LCD screen controls the light pattern. An image of each layer is generated on the LCD screen, and an entire layer can be hardened at once, similar to DLP.

Stereolithography, aka vat photopolymerization or VPP, the first ever 3D printing technology, has ramified into many different evolutions.
Difference between the leading vat photopolymerization technologies. Image credit: ANIWAA.

Because LCD 3D printing uses an LCD screen and not a projector to create images of the layers and photopolymerize the liquid resin, no special device is required to direct the light. This makes systems based on LCD technology much more affordable, especially for smaller parts, as the print quality of an LCD printer depends on its LCD density. The more pixel density it has, the better the print quality.

The LCD screen serves as a black-and-white matrix, allowing light to enter and cure the polymer to create each layer of the finished part. The resin is contained in a vat and hardens into functional plastic when selectively exposed to light. LCD printers can produce products using a “bottom-up” process, where the object is printed layer by layer and attached to the print platform, rising out of the resin bath. This process is repeated until the object is complete.

Key players and systems

LCD 3D printers are considered an ideal and affordable vat photopolymerization solution for various dental applications due to their ability to offer high resolutions on small parts. Companies such as Asiga and Ackuretta offer both standard DLP and LCD systems, with the latter specifically targeting the dental segment.

Another key trend in LCD technology is the availability of ultra-low-cost systems, mainly developed and marketed by Chinese companies such as Falshforge, Creality, and Elegoo. Anycubic is the market leader in this segment, with the Photon Mono series providing reliable and high-resolution 3D printing capabilities starting at just $199 (build volume: 130 x 80 x 165mm).

Photocentric’s Magna 3D printer

In 2011, Australian company Asiga launched the world’s first LED-based DLP 3D printer, sparking the affordable desktop stereolithography revolution. This revolution continued with UK-based company Photocentric, which received a UK Government Innovate grant in 2014 to develop a novel type of 3D printer that could cure daylight photopolymers using LCD screens. The company uses internally developed daylight-activated resins to work with LCD screens and refers to its technology as Daylight Polymer Printing (DPP). In 2016, the company introduced the Liquid Crystal 10 3D printer, the world’s first daylight hardening 3D printer. In 2019, Photocentric launched the Liquid Crystal Magna, its largest printer to date. This was followed in 2021 by the LC Opus, its fastest LCD printer.

Today, numerous manufacturers are offering LCD 3D printers. For example, Ackuretta also offers the SOL, featuring a unique 54-LED panel and dynamic optical light engine that only cures the printing area, prolonging the lifespan of the LCD screen while ensuring accurate prints and minimizing the need for user maintenance. Another Taiwanese company, Phrozen, has emerged as a leader across various segments, from professional to consumer. In early 2022, the company introduced its most ambitious system, the Sonic Mega 8K, priced at just $1,700.

Table of key players and systems in LED/LCD stereolithography
CompanyLocationPolymer AM Hardware ProductsType of products
PhotocentricUSA/UKLC Magna, LC OpusIndustrial and professional
AsigaAustraliaMAX/MAX UVProfessional
AnycubicChinaPhoton seriesProsumer and consumer
PhrozenTaiwanSonic seriesProfessional, prosumer and consumer
PrusaCzech RepublicSL1SProsumer

Continuous DLP stereolithography/high-speed vat photopolymerization

Continuous DLP technology is an interesting area of development in vat photopolymerization technology, and it is considered one of the most exciting areas in additive manufacturing as a whole. While the base technology still relies on DLP, these systems belong to a different category of machines due to their significantly higher production speeds and the durability of the materials used.

This family of technologies is commonly known as continuous DLP (cDLP) because it accelerates the vat photopolymerization process across layers using a membrane. In other words, instead of projecting an image of each layer like conventional DLP technology, continuous DLP technology projects a “movie” across multiple layers. This approach offers several advantages, including up to 100 times faster production compared to conventional vat photopolymerization and the production of parts with smooth surfaces. Hence, these technologies are also referred to as “layerless photopolymerization” and “high-speed photopolymerization.”

Continuous DLP technology was first patented by Al Siblani of EnvisionTEC in 2006. However, the first company to successfully commercialize a high-speed photopolymerization system, and the current market leader, is Carbon, based in Silicon Valley. Carbon was co-founded by Joseph DeSimone, a university professor who is one of the few individuals to have been elected to all three branches of the US National Academies. Prior to Carbon, speed was not a significant concern for DLP technology because the photopolymer resins used were not durable enough for producing final parts. DeSimone had the insight to mix durable thermosets such as polyurethane with enough photopolymerizable material to enable the curing reaction. With these materials, it became feasible to accelerate the process. Although Carbon took a significant lead in this area, many other similar systems are now available in the global market.

The heart of the CLIP process that powers DLS technology is the “dead zone”—a thin, liquid interface of uncured resin between the window and the printing part. Light passes through the dead zone, curing the resin above it to form a solid part without curing the part onto the window. Resin flows beneath the curing part as the print progresses, maintaining the “continuous liquid interface” that powers CLIP and avoiding the slow and forceful peeling process that is inherent to many other resin-based printers.

To understand how continuous DLP processes work, we can take as an example of high-speed DLP the pioneering Digital Light Synthesis (Carbon DLS). This process is powered by their Continuous Liquid Interface Production (CLIP) technology. CLIP is a photochemical process that involves projecting light through an oxygen-permeable window into a reservoir of UV-curable resin. As a sequence of UV images is projected, the part solidifies, and the build platform rises.

At the core of the CLIP process is the concept of the “dead zone.” This refers to a thin, liquid interface of uncured resin located between the window and the part being printed. Light passes through this dead zone and cures the resin above it, resulting in the formation of a solid part without the part getting stuck to the window. As the print progresses, the resin continues to flow beneath the curing part, ensuring a “continuous liquid interface” that powers CLIP. This eliminates the need for the slow and forceful peeling process used in many other resin-based printers.

Carbon was the first company to incorporate heat-activated programmable chemistry into its materials. After a part is printed, it undergoes a secondary chemical reaction when baked in an oven, leading to material adaptation and strengthening. This process enables the production of high-resolution parts with mechanical properties comparable to those of engineering-grade materials.

As another example, 3D Systems Figure 4 technology uses a special air-permeable film to separate the resin from the laser mechanics. A vacuum system locks down the built plate, and the permeable layer allows the natural formation of a 10 micron air layer on the wet side of the film. Which makes it unnecessary to pump air through the film.

3D Systems’ Figure 4

Yet another approach to high-speed VPP was presented by the Austrian startup Cubicure, which dental aligner giant Align Technology recently acquired. Cubicure’s Hot Lithography technology uses a special heating mechanism that processes even extremely viscous materials. This expanded process window has already facilitated the development of many new photopolymer.

Key players and systems

In today’s market, a few companies, primarily based in the US, are marketing high-speed 3D printers. These companies include Carbon, which leads the segment, along with major players in the overall 3D printing market such as Stratasys (Origin) and 3D Systems, as well as Desktop Metal, Nexa3D, Luxcreo, Cubicure, and Carima.

Carbon’s DLS technology has been used by Adidas to manufacture millions of generatively designed midsoles for the Futurecraft 4D brand. It is also employed by Ford and Lamborghini in the production of automotive parts and components. The technology is now making headway in the dental segment as well, although the company experienced a slowdown in 2023.

The Envision One cDLM 3D printer from ETEC (Desktop Metal)

Following EnvisionTEC’s acquisition by Desktop Metal, the Envision ONE high-speed cDLM (continuous digital light manufacturing) 3D printer became part of the company’s offerings for both the industrial and healthcare sectors. In the industrial sector, it is utilized for jewelry, consumer products, and other final parts under the ETEC brand, while in the healthcare sector, it is provided through the Desktop Health brand for medical and dental applications.

Another player in high-speed photopolymerization technologies is 3D Systems. Its Figure 4 systems leverage a UV- and heat-based curing process for rapid polymerization. 3D Systems claims that this technology enables the fastest additive manufacturing throughput and time-to-part in the world. Figure 4 production part prints can achieve speeds of up to 100 mm/hour, offering high part accuracy and Six Sigma repeatability across all material productions. Stratasys entered the segment in 2020 when it acquired San Francisco startup Origin. The company wanted to capitalize on vat photopolymerization for production, and Origin’s Programmable Photopolymerization (P³ or PPP) technology was the perfect fit. Origin developed this technology to achieve high throughput, repeatability, and on-demand production. To maximize production capacity per available surface, Stratasys plans to leverage the small-footprint modular Origin One printers.

Nexa3D’s XiP printer

Based in California, Nexa3D is a company co-founded by Avi Reichental, former CEO of 3D Systems and a pioneer in the AM industry. Today, Nexa3D is emerging as a leading manufacturer of high-speed photopolymerization 3D printers. This success can be attributed to its proprietary Lubricant Sublayer Photo-curing (LSPc) technology and patented structured light matrix. The NXV printer by Nexa3D can reach speeds of up to 10 mm per minute. Similar to other continuous digital light processing (DLP) processes, Nexa3D’s LSPc utilizes a membrane that creates a no-stick zone between the printed part and the vat, enabling faster print speeds.

LuxCreo, another high-speed photopolymerization company with headquarters in the San Francisco Bay Area and Beijing, focuses on smart factory additive production capabilities and Digital 3D Production Lines to bring new ideas to market faster. LuxCreo’s Digital 3D Production combines their ultra-fast LUX3 3D printers, LEAP (Light Enabled Additive Production) high-speed DLP technology, materials, and software to provide a connected, agile, and scalable 3D printing production network. With over 200 printers in their global installed base, LuxCreo offers clients access to their Smart Factory 3D printing production service. The company is targeting both the dental and consumer products markets, including footwear and sports equipment. LuxCreo already supports companies such as ASICS and Puma through their production service network.

Cubicure, the only European contender in the production vat photopolymerization segment, is based in the technological AM hub of Vienna, Austria. In 2023, the company was acquired by Align Technology, the leader in the dental aligners market. This acquisition was made to start internal production of dental aligner forming tools. Cubicure’s patented Hot Lithography technology is based on a heating and coating mechanism capable of safely and precisely processing highly viscous resins and pastes at working temperatures of up to 120 °C.

Carima, a Korean company, was among the first to develop high-speed photopolymerization 3D printers using their proprietary C-CAT (Carima-Continuous Additive Technology) in 2015. The latest C-CAT model, released in 2020, has been improved to print faster and more accurately in continuous layers. However, the company has been quiet since 2022. On the other hand, NewPro, a Canada-based company, has exited the market.

Table of key players and systems in continuous DLP
CompanyLocationPolymer AM Hardware ProductsType of products
CarbonUSAM1, M2, L1Industrial and professional
Desktop Metal (ETEC, Desktop Health)USAEnvision ONE CDLM, Vida CDLM, Micro Plus CDLMProfessional
Nexa3DUSANXE 400, NXD 200, XiPIndustrial, professional and prosumer
3D SystemsUSAProduction, Modular, Stand-alone, Jewelry, DentalIndustrial and professional
Stratasys (Origin)USA/IsraelOrigin OneIndustrial and professional
LuxCreoUSA/ChinaLux series, ILUXIndustrial, professional and prosumer

Micro and Nano Stereolithography: 2PP and µSLA/µDLP

Another significant area of development in stereolithography is within technologies that are capable of achieving microscopic and nanoscopic resolutions. These two differ significantly. Most microscopic stereolithography, which can achieve resolutions of a few microns, is accomplished via optimized DLP stereolithographic systems, while nanoscopic resolutions (of a few tens of nanometers) are achieved using a process called two-photon polymerization (2PP) or multiphoton lithography.

Much like standard stereolithographic DLP technologies, micro stereolithography (µSL) leverages a DLP light engine along with precision optics, motion control, and advanced software to produce parts in layers using a photochemical process. A photosensitive liquid resin is exposed to light so that polymeric cross-linking and solidification occurs. In projection-based µSL technology, a flash of ultraviolet (UV) light causes the rapid photopolymerization of an entire layer of resin. Digital microdisplay technology provides dynamic stereolithography masks that work as a virtual photomask. This technique allows for rapid photopolymerization of an entire layer with a flash of UV illumination at micro-scale resolution. The mask can control individual pixel light intensity, allowing control of material properties of the fabricated structure with desired spatial distribution.

Stereolithography, aka vat photopolymerization or VPP, the first ever 3D printing technology, has ramified into many different evolutions.
By means of an objective lens, with Two-Photon Polymerization a pulsed laser beam is focused into a very tight volume inside a photosensitive material. Even though the average power of the laser might seem quite low, the laser emits ultrashort light pulses that contain a high photon density. Credits: Nanoscribe.

Two-Photon (or Multiphoton) lithography or 2PP is a technique for creating small features in a photosensitive material without the use of complex optical systems or photomasks. It relies on a multiphoton absorption process in a material that is transparent at the wavelength of the laser used for creating the pattern. By scanning and properly modulating the laser, a chemical change (polymerization) occurs by absorption of two photons at the focal spot of the laser and can be controlled to create a three-dimensional pattern with no geometric limitations.

The photo-material is transparent at the wavelength used by a pulsed laser, so nothing happens in the focalization cone. However, at the focal spot only, the photo-material can simultaneously absorb two photons within the volume of a single voxel. A chemical reaction starts, and the liquid monomer becomes a solid polymer inside the voxel. In addition, because the laser can go through polymerized parts, any 3D shape can be created, including overhangs without supports, complex internal structures, and hollow channels.

Key players and systems

Stereolithography-based and 2PP micro and nano 3D printers are available today from companies such as Nanoscribe (part of BICO), Boston Micro Fabrication (BMF), Fabrica Group (part of Nano Dimension), UpNano, and MicroLight3D, among others. BMF uses PμSL (projection micro stereolithography), a type of DLP, to produce industrial parts with a printing resolution of 2μm and a tolerance of +/- 10µm. The company’s ultra-high-resolution 3D printers, known as the microArch series, have resolutions ranging from 25μm to just 2μm. The microArch P-130 and microArch S-130 models are the highest-resolution 3D printers available.

The Fabrica Tera (25, 250), Giga (25, 250) micro SLA 3D printers from Nano Dimension.

Another major player in the micro 3D printing segment is Nano Dimension, which acquired Nanofabrica in 2021. Nano Dimension focuses on precision digital manufacturing and offers the Tera and Giga lines of 3D printers that use Micro Adaptive Projection (MAP) technology. These systems combine semiconductor lithography, advanced optics, and 3D printing to achieve a resolution of 2μm. The Giga version also offers a large build volume of up to 60 x 52 x 160 mm, allowing users to print one large and ultra-precise part or multiple micro parts on the same build plate to complete the manufacturing process of hundreds of parts in a single night shift.

Nanoscribe, a Germany-based company that is now part of the BICO group, was the first to introduce a nano 3D printer based on 2PP technology. Founded as a spin-off of the Karlsruhe Institute of Technology (KIT), Nanoscribe has over 3,000 active users in more than 30 countries and is profitable. The company’s Photonic Professional GT and Photonic Professional GT2 systems can produce intricate structures of various 3D shapes, including crystal lattices, porous scaffolds, naturally inspired patterns, smooth contours, sharp edges, undercuts, and bridges. In 2021, after being acquired by BICO, Nanoscribe introduced the Quantum X series of 2PP 3D printers that offer 3D microfabrication capabilities alongside the company’s Two-Photon Grayscale Lithography (2GL) technology for surface patterning.

Stereolithography, aka vat photopolymerization or VPP, the first ever 3D printing technology, has ramified into many different evolutions.
Nanoscribe’s Photonic Professional GT2 for 2PP.

Another company that has developed a 2PP-based system is UpNano, based on research conducted at the Technical University in Vienna (TU Wien). UpNano’s NanoOne and NanoOne Bio high-resolution 3D printing systems provide the highest resolution in the sub-micrometer range and are marketed as the fastest high-resolution 3D printing systems on the market. These machines, based on multiphoton lithography, combine the precision of 2PP technology with a throughput of up to 200 mm³ per hour. This makes the system suitable not only for scientific research and multi-user facilities but also for batch and small-series production of micro parts used in various industries.

Yet another increasingly relevant player in the nanoscale printing sector is MicroLight3D, a French company that originated from Grenobles Alpes University (UGA). Its technology is based on non-linear two-photon absorption, which is utilized to produce a solid 3D printed structure using a photoactive material. Additionally, MicroLight3D offers the Smart Print UV, a micro stereolithography system based on maskless lithography. The microFAB-3D 3D printer from MicroLight3D uses lasers controlled by proprietary software to create solid structures with a voxel diameter as small as 0.2 µm. Various materials such as photopolymers, biocompatible substances, proteins, and other biomaterials can be used in this printer. Notably, the unique aspect of the microFAB-3D system is its use of a green laser with a wavelength of 532 nm. MicroLight3D also developed a specialized material called “Green-A,” a polymer optimized for the green wavelength. This material offers ultra-high resolution and rigidity. The higher resolution of the green wavelength (532 nm) compared to the red wavelength (800 nm) is directly proportional to the wavelength.

Table of key players and systems in micro VPP
CompanyLocationPolymer AM Hardware ProductsType of products
Nano Dimension (Fabrica)IsraelTera (25, 250), Giga (25, 250)Industrial
Boston Micro Fabrication – BMFUSAmicroArch series (2μm, 10μm, 25μm)Industrial
BICO (Nanoscribe)GermanyPhotonic Professional GT2, Quantum X seriesIndustrial and professional
UpNanoAustriaNanoOne, NanoOne BioProfessional
Microlight3DFranceMicro-FAB 3D, Smart Print UVProfessional

A look at the VPP market of today

The vat photopolymerization segment is by far the most diverse within polymer AM hardware. One significant insight is that within just a few years LCD-based systems, which are a lower-cost variation of DLP systems and part of the stereolithography family, have quickly become and continue to be the dominant segment in terms of unit sales. They represent over 85% of the market, with over 170,000 units sold yearly as shown in the chart below. This is due to the rapid consumer market penetration of ultra-low-cost systems (sub $300) from Chinese manufacturers, along with thousands of prosumer-level systems based on LCD technology, all the way up to production-level machines.

Laser stereolithography is the second-largest segment in 3D printing, driven by the adoption of both professional and industrial-grade systems. Projector-based DLP technology and continuous DLP technology are diverging paths. The former, established in small part markets like dental and jewelry, is plateauing in adoption. The latter is expanding into serial and mass production but is still in an early phase of development.

Two-photon polymerization (2PP) and micro stereolithography (µSLA) are notable technologies. 2PP systems are primarily for research and represent a niche but growing market. Meanwhile, µSLA hardware is gaining traction for producing microscopic components.

In terms of revenues, the vat photopolymerization (VPP) market shows fragmented and varied technological approaches. The main subsegment within VPP is laser stereolithography (SLA), which was the first AM technology to be invented. Currently, 3D Systems dominates the high-end industrial SLA market, while Formlabs dominates the professional market. However, Chinese manufacturers are experiencing significant growth in this area, particularly in Asia but also in other regions. In 2022, SLA hardware accounted for more than half of the vat photopolymerization market revenues.

Stereolithography, aka vat photopolymerization or VPP, the first ever 3D printing technology, has ramified into many different evolutions. The other relevant revenue segment within VPP is digital light processing (DLP), where a planar digital light projection replaces the laser. DLP is divided into three major subsegments. Traditional DLP is commonly used for high-precision parts in prototyping, dentistry, jewelry, and some healthcare applications such as hearing aids. Layerless, continuous, or high-speed DLP utilizes an oxygen membrane to accelerate the build process using hybrid materials that combine photopolymers and thermosets to produce final parts. LCD systems form the third DLP subsegment, typically comprising lower-cost systems that are sold in high unit quantities.

The VPP production market of tomorrow

Conventional laser stereolithography (SLA) remains the most important AM technology for industrial and prosumer/professional systems. The market leader for this technology is 3D Systems, but it faces increasing competition from Chinese manufacturers that are developing larger industrial systems. Formlabs is driving the professional segment and sells the most SLA systems overall. We project that this subsegment will grow from about 25 thousand units sold in 2022 to nearly 90 thousand units sold yearly by the end of the forecast period.

The next subsegments in vat photopolymerization belong to the digital light processing (DLP) family. Standard DLP is a process that is more expensive for larger parts but more precise for multiple smaller parts. Its adoption is driven by its use in segments such as dental, jewelry, and prototyping. The forecast predicts a nearly fivefold growth in unit sales by 2032. Growth in the high-throughput production version of DLP technology is expected to be driven by increasing competition from other market operators and lower overall material prices, although the high cost of the hardware poses a limitation.

In this edition of our Polymer AM Market report, we considered micro stereolithography (VPP – μSLA) and 2PP as stand-alone segments. This vat photopolymerization technology is experiencing significant growth in adoption, and we predict that yearly sales will increase significantly. Currently, these sales are represented by high-end industrial machines, but smaller and more affordable machines may also offer these capabilities in the future, potentially taking market share away from conventional SLA and the DLP subsegments.

Stereolithography, aka vat photopolymerization or VPP, the first ever 3D printing technology, has ramified into many different evolutions. In the future high-speed DLP and SLA will be the largest revenue segments in vat photopolymerization. By 2032, high-speed DLP will be in fact surpass SLA as the largest vat photopolymerization hardware revenue opportunity overall totaling $2.7 billion in yearly revenues.

Beyond SLA, which will grow to over 2.4 billion in revenues by 2032, among the key sub-technologies of vat photopolymerization, conventional DLP (VPP-DLP) systems are expected to generate $601 million by 2032, whilst VPP-LCD systems are expected to grow to almost $1 billion by the end of the forecast period.

The installed base of vat photopolymerization systems is already substantial, and growth rates are expected to be lower due to the obsolescence of low-cost LCD systems. However, the installed base of industrial systems is predicted to grow rapidly in the second half of the forecast period, driven by increased adoption of VPP technologies for part production.

As can be expected, the majority of the installed base of vat photopolymerization systems comprises low-cost LCD systems, totaling 1.7 million machines installed worldwide in 2022. VoxelMatters projects this category to remain the largest within vat photopolymerization, with almost 12 million units installed by 2032. Altogether 

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Davide Sher

Since 2002, Davide has built up extensive experience as a technology journalist, market analyst and consultant for the additive manufacturing industry. Born in Milan, Italy, he spent 12 years in the United States, where he completed his studies at SUNY USB. As a journalist covering the tech and videogame industry for over 10 years, he began covering the AM industry in 2013, first as an international journalist and subsequently as a market analyst, focusing on the additive manufacturing industry and relative vertical markets. In 2016 he co-founded London-based VoxelMatters. Today the company publishes the leading news and insights websites VoxelMatters.com and Replicatore.it, as well as VoxelMatters Directory, the largest global directory of companies in the additive manufacturing industry.

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